Cellular communications systems continue to grow in popularity and have become an integral part of both personal and business communications. Cellular telephones allow users to place and receive voice calls most anywhere they travel. Moreover, as cellular telephone technology has increased, so too has the functionality of cellular devices and the different types of devices available to uses. For example, many cellular devices now incorporate personal digital assistant (PDA) features such as calendars, address books, task lists, etc. Moreover, such multi-function devices may also allow users to wirelessly send and receive electronic mail (email) messages and access the Internet via a cellular network and/or a wireless local area network (WLAN), for example.
Accordingly, because of the widespread use and reliance on cellular devices, many users carry their cellular devices on their person much of the day, and place them on their desks at work. Yet, since cellular devices are frequently communicating with a cellular network even when a user is not participating in a phone call, they are frequently emitting radio frequency (RF) signals. When in close proximity to a land line telephone, such as a private branch exchange (PBX) phone in a workplace, these RF signals may cause interference which results in an audible buzz or other undesirable sound by the PBX phone.
Certain PBX telephone devices have generally attempted to address interference from other sources. By way of example, U.S. Pat. No. 6,473,495 to Willer is directed to a home network environment implemented in a customer premises having a PBX for outputting analog telephone signals onto twisted pair wiring arranged in a star topology. This is done by adding a high pass filter in parallel along the twisted pair wiring. The high pass filter enables transmission of network data signals between the telephone line pairs connected to the PBX without interference of the switching operations by the PBX of analog telephone signals. The high pass filter may be implemented within the PBX, or added externally to the PBX system as a retrofit for existing customer premises.
Despite such attempts to address certain interference problems in PBX telephone systems, further protection may be required to significantly mitigate the effects of RF interference from a nearby cellular device, for example.